Total hip and knee replacements (THRs and TKRs) now are among the most common major surgical procedures performed in the US. Research to date suggests that in-home and other forms of outpatient therapy are as effective as inpatient post-operative rehabilitation for most patients. Indeed, the share of Medicare beneficiaries with THRs and TKRs discharged to home health care is rapidly increasing with roughly a third of each group now discharged to home health care. Nevertheless, almost nothing is known about: the patient, provider and market characteristics associated with different utilization patterns and outcomes; whether more intensive home health therapy leads to the better functional outcomes; or the cost implications of more intensive home health therapy. Thus, the need is great and time ripe to conduct secondary analyses of existing data sets, with separate analyses of THR and TKR patients, to achieve the following aims: ? Aim 1. Describe and compare patient clinical and sociodemographic factors (e.g., functional status prior to surgery, medical comorbidities, living arrangements), hospital and home health provider characteristics (e.g., for-profit status, years of Medicare program participation) and market factors (e.g., historical home health use per Medicare beneficiary, managed care penetration rate) associated with post-acute utilization patterns and outcomes during the 6-month (180-day) period following index hospital stay discharge ? Aim 2. Compare the effectiveness of higher vs. lower intensity home health rehabilitation therapy with higher intensity defined as an average of 4+ visits per week up to the week of discharge; and ? Aim 3. Compare the Medicare costs of patients receiving higher vs. lower intensity home health rehabilitation therapy for a 6-month (180-day) period following index hospital stay discharge the proposed study will exploit variation in current clinical practice observed in 2013-2014 national Medicare data. An instrumental variables approach will be used to correct for non-random assignment of patients to different therapy levels. Major strengths of the proposed study include preliminary research informing the definition of intensive home health therapy and an outstanding team of researchers with expertise in orthopedic surgery, geriatrics, home-health therapy, econometrics and health services research. Together, we have in- depth knowledge of the study procedures and post-acute therapy, as well as experience developing analytic files from Medicare claims and patient assessment data, and implementing rigorous comparative effectiveness methods. Now is the time to answer critical questions about the effectiveness of higher versus lower intensity home health rehabilitation therapy, producing timely results that can be spread rapidly using national channels of communication built into the study design? Findings from the proposed research project have the potential to directly benefit medical decision makers, policymakers and -- most importantly -- the growing number of older adults needing lower extremity joint replacements to remain mobile and live independently in the community.